In false-twisting equipments, the length of a yarn heater has been increased with elevation of the yarn travelling speed. In the case where a yarn taken out from a yarn feed bobbin is passed through a vertical first heater, there is often adopted a method in which after the yarn is taken out from the upper portion of the vertical first heater, the moving direction of the yarn is changed by a guide pin and is transferred to the opposite side of an operation space. The yarn is false-twisted by a false-twisting device disposed in the upper portion of the operation space. In false-twisting equipment of this type, the first heater has a certain length determined depending on the yarn speed and heater temperature required for setting twists, and the height of this heater is much larger than the height of a second heater or winding device disposed on the opposite side of the operation space. Accordingly, the bending angle of the yarn bent toward the operation space in the upper portion of the first heater becomes acute, with the result that propagation of twists is inhibited and the yarn speed has to be controlled to a low level.
In this false-twisting equipment, a false-twisting spindle, a balloon control device, a cooling device and the like are disposed to treat the yarn which passes across the operation space in the upper portion thereof. Unless the yarn passes through these devices substantially in a straight line, the yarn quality is degraded.
The above-mentioned yarn guide pin disposed in the upper portion of the first heater is contaminated by smoke formed from the heated yarn and rising and escaping from a preheater and also contaminated by the yarn which is brought into frictional contact with the guide pin. If the yarn is hung on such contaminated guide pin and travelling of the yarn is started, the yarn is readily broken by a large frictional force produced at the point of contact between the guide pin and yarn.